Re: Uses for memory barriers

[Paul E. McKenney]

On Wed, Sep 20, 2006 at 03:51:29AM +1000, Nick Piggin wrote:
> Alan Stern wrote:
> >On Wed, 20 Sep 2006, Nick Piggin wrote:
> 
> >>I don't think that need be the case if one of the CPUs that has written
> >>the variable forwards the store to a subsequent load before it reaches
> >>the cache coherency (I could be wrong here). So if that is the case, then
> >>your above example would be correct.
> >
> >I don't understand your comment.  Are you saying it's possible for two 
> >CPUs to observe the same two writes and see them occurring in opposite 
> >orders?
> 
> If store forwarding is able to occur outside cache coherency protocol,
> then I don't see why not. I would also be interested to know if this
> is the case on real systems.

We are discussing multiple writes to the same variable, correct?

Just checking...

							Thanx, Paul
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